There are several methods like you describe. One common method is to have it face-mounted onto the back side of plexi and then floated off the wall with a piece of aluminum bar on the back. I have some done this way without the plexi, just mounted onto a piece of rigid Sintra plastic with an aluminum frame adhered to the back so it sits an inch off the wall. It looks good. I should add a shameless plug that I am writing a textbook on contemporary mounting and display techniques for photographs.